1. Field of The Invention
The present invention relates to an apparatus and method for determining an engine revolution displacement for a multi-cylinder four-stroke internal combustion engine, an engine operation being controlled on the basis of the determined engine revolution displacement.
2. Description of The Background Art
Conventionally, a crank angle sensor of either photo-electrical pick-up or electromagnetic pick-up type is disposed on a member rotated in synchronization with engine revolutions in order to detect the engine revolution angular displacement used to control a fuel injection start timing of the engine or to control an ignition timing. The crank sensor has two functions: one of the functions outputting a reference signal (REF) which corresponds to a predetermined crankshaft angular displacement (position) (for example, 110.degree. BTDC (Before Top Dead Center)) with respect to a top dead center in each one of the engine cylinders, the reference signal being output whenever the engine crankshaft has rotated through a predetermined crank angle set according to the number of cylinders (for example, in a case of the six-cylinder engine, 720.degree./6=120.degree.) and the other function outputting a unit angular signal (POS) whenever the engine crankshaft has rotated through a unit angle of the crank angle (for example, 1.degree. or 2.degree.).
Hence, when a control unit connected with the crank angle sensor counts a number of the unit angular signal (POS) upon the start of the reference signal (REF), the control unit determines the engine revolution position nd uses the determined engine revolution position for the control of either the fuel injection start timing or the ignition timing for each spark plug installed for a corresponding one of the engine cylinders.
Since the engine revolution position is determined with the reference signal output from the crank angle sensor as the reference in the above-described engine revolution displacement determining apparatus, however, the determination of the engine revolution displacement becomes disabled if one or more of the reference signal is not received due to, for example, a disturbance. Consequently, during the engine operation control operation, either of the fuel injection or the ignition for one of the engine cylinders corresponding to a lost present reference signal cannot be carried out so that an engine revolution becomes out of order.